has anyone thought about combining a J tube of a rocket mass heater into a gasifier i have seen a few threads where heat is melting nozzles and grates perhaps a rocket stove in its principal operation of at the 90 degree bend the gasses swirl focusing unburnt tar and fuel into its self im amazed at how well they work very little ash and smoke and people have made self feeding devices for pellet operation im thinking that a person could draw off the gasses just before reaching the 90 one thing im impressed by with rocket mass heaters is the ability to stay cool as the flame moves though the burn tube it draws in fresh cool air if somehow you could capture the gas along this tube it might solve the heat issue of melting even hard metals even in charcoal simple fire
Hi Ryan, welcome to the site. An interesting idea. I like rockets myself but the problem I think you would have is without the secondary burn on a rocket stove I do not think you would develop the vacuum pressure that produces the suction/rocket action of the rocket stove. The nozzle melting problems on charcoal gasifiers can be beaten using exhaust recirculation or water drip. My tractor used a 3/4 inch hole in a refractive cement base and was still working fine after going on 50 hours… I never could figure out a way to make the horizontal nozzle survive but others did.
Cheers, and welcome to drive on wood.
Welcome. 
It is an interesting way to think about it. What you would end up with is have is a essentially an open top cross-draft gasifier.
Now what -might work, and I will leave it to debate, but if you had the L, and put a nozzle inlet on horizontal part of the L, filled the horizontal part and sealed the top, with a gas exit.
Then what you have is a small nozzle feeding air space that opens up really wide before it hits the char bed that is sitting on the bottom at the 90. But that might create a venturi effect and draw gases into the horizontal part by the nozzle to be closer to the oxygen. It might work with charcoal because the heat would be sucked through the charbed. I don’t think it would work with wood without a lot of tar.
As always, the only real way to find out is try it! Maybe you have stumbled onto something!
i figured i would toss it out there for someone else that can experiment
i was watching a rocket device i had made a combo of a dakota firehole and a n old cast iron 90 and observed that the fire drawed air and didnt mix until it hit the 90 this let the intake tube stay cool
flame and air move in a similar way if at the end of the vertical tube is where the gas was collected so take a down draft turn it side ways add a 90 and keep the hot 90 outside collect the gass after this point or maybe before it?
when them build rocket mass heaters the use a drum at the top/end of the fire tube that causes the flame and heat to hit the top and cooler gas to fall down the sides then though cob that stores the remaining heat from my understanding the magic happends in the 90 and the top part of the barrel im amazed at the low ash and tar/smoke evidently what doesn’t burn up in the 90 is suspended in the upper portion of the barrel causeing a more complete burn and ash falling out of suspension at this point
It is a good observation. It would probably require quite a bit of messing around with it to get the parameters right. It sounds like you have quite a bit on your plate already and can use something that works now.
Another option for nozzles was the boron/silicon ones.